Pierre Andrews 


Testing an Option value without the gymnastics

In Boolean Operators for Option, I have shown how to simply build test for the existence of an Option. Go check it out, the idea is simple and allows to write:

val opt1 = Some("string")
val opt2 = None

if(opt1 && opt2) ...

instead of the longer if(opt1.isDefined && opt2.isDefined) .... It's just a way to write things in a more straightforward maner.

But what if you want to also test what's in the Option? You can use a match construct if you have only one option, but when you are mixing different things (like optional parameters), writing a match is a bit cumbersome and if is often more direct.

Let's say that you have an optional parameter to a request, which is a string representing a special view. In addition to this optional parameter, you also have to test if you have a valid user ID in the request. You can do something like:

def request(userID: Long, view: Option[String]) {
    validateUser(userID) match {
        case None => ...
        case Some(user) if view && view.get.equals("details") => ...
        case Some(user) => ...
    }
}

this view && view.get.equals("details") is a bit cumbersome, but Option following the collection API, you can use a very nice shortcut to write all this:

case Some(user) if view.exist(_.equals("details")) => ...

The exist function only returns true if the Option is Some and the predicate you are providing returns true. Here is what the doc says:

Returns true if this option is nonempty and the predicate p returns true when applied to this scala.Option's value. Otherwise, returns false.

That's it. The exists name might be a bit confusing, so you could write an alias:

  implicit class RichOpt[T](opt: Option[T]) {
    def assert(p: T => Boolean): Boolean = opt.exists(p)
  }

or even, if you only deal with String in the Option:

implicit class StrOpt(opt: Option[String]) {
      def strEquals(s: String): Boolean = opt.exists(_.equals(s))
  }

that you can use:

  val opt1 = Some("string")      //> opt1  : Some[String] = Some(string)
  opt1.assert(_.equals("test"))//> res0: Boolean = false
  opt1.strEquals("string")       //> res1: Boolean = true